Noise generated by aircraft is an important problem. Aircraft noise is unpleasant for aircraft passengers, and for persons in the vicinity of aircraft. Aircraft noise is also unpleasant for persons around airports, including those in the flight paths leaving or approaching airports. The problem of aircraft noise is so significant that federal regulations directed to limiting the noise that may be generated by individual aircraft have been enacted. As airports and communities become more congested, more demanding regulations can be expected, making it more difficult for aircraft to meet the regulations.
The majority of the noise generated by an aircraft is produced by aircraft engines. Modern aircraft used for commercial transportation over relatively long distances almost exclusively employ turbo-fan jet engines, namely, high by-pass turbo-fan jet engines.
Air flow entering a high by-pass turbo-fan jet engine, is divided into a primary air flow that passes through the engine core, and a secondary air flow that flows around, or "by-passes" the engine core. A significant amount of noise is believed to emanate from the primary air flow as it passes from the fan rotor through the low compressor inlet guide vanes of a high by-pass turbo-fan jet engine. Additional noise is believed to emanate from the primary flow as it passes from the low compressor inlet guide vanes, through the low compressor rotor.
Past attempts to control noise in high by-pass and other types of turbo-fan engines have generally been directed to acoustically lining the engine nacelle. Unfortunately, acoustic lining has little effect on noise emanating from the primary air flow through the engine core because the acoustic lining is spaced too far away from this significant noise source to be effective. Further, acoustic lining in the nacelle does not impede the path of acoustic waves forward emanating from the engine interior. The present invention provides an improved solution for controlling noise emanating forward from the interior of high by-pass and other types of turbo-fan jet engines.